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This work reports the synthesis and characterization of mesoporous silica nanoparticles (MSNs) functionalized with tridecafluorooctyltriethoxysilane (F13) and their in situ incorporation onto cotton textiles. The hybrid MSNs and the functional textiles were prepared by a one-pot co-condensation methodology between tetraethylorthosilicate (TEOS) and F13, with hexadecyltrimethylammonium chloride (CTAC) as the template and triethanolamine as the base. The influence of the F13 to TEOS molar ratio (1:10, 1:5 and 1:3) on the nanoparticle morphology, porosity, degree of functionalization, and hydro/oleophobic properties is discussed. The hybrid nanosilicas presented high colloidal stability and were spherical and monodispersed with average particle size of ∼45 nm. They also showed high surface areas, large pore volumes, and a wormhole-type mesoporous structure. The increase in the organosilane proportion during the co-condensation process led to a more radially branched wormhole-like mesoporosity, a decrease in the surface area, pore volume, and amount of surface silanol groups, and an enrichment of the surface with fluorocarbon moieties. These changes imparted hydrophobic and oleophobic properties to the materials, especially to that containing the highest F13 loading. Cotton textiles were coated with the F13-MSNs through an efficient and less time-consuming route. The combination between surface roughness and mesoporosity imparted by the MSNs, and the low surface energy provided by the organosilane resulted in superhydrophobic functional textiles. Moreover, the textile with the highest loading of fluorocarbon groups was superamphiphobic.

Granular multilayers [Fe(t nm)/MgO(3 nm)]N with 0.4 nm≤t≤1.5 nm were prepared by sequential pulsed laser deposition. Transmission electron microscopy (TEM) images show that increasing t causes the growth of the sizes of Fe nanoparticles and broadening of the particle size distribution. For t>0.81 nm, continuous Fe layers are formed. The evolution of the shapes and sizes of the particles is reflected in the magnetic properties of the investigated films. A crossover from superparamagnetic to ferromagnetic behavior upon formation of a continuous Fe layer is observed. The fit of zero field cooled and field cooled susceptibility measurements and magnetization curves using Curie–Weiss law and a weighted sum of Langevin functions, respectively, allows the estimation of the average granule size for the films with t<0.61 nm. The results of the estimations correlate with the data obtained from TEM images. Reduction of saturation magnetization for Fe nanoparticles and an increase of the coercivity up to 1200 Oe at low temperatures were found. It is attributed to the formation of Fe-core/FeOx-shell structured nanocrystals. The oxide shell gives rise to a strong contribution of surface anisotropy. Isotropic tunneling magnetoresistance up to ∼3% at room temperature and in magnetic field up to 18 kOe was found for the film with t=0.61 nm. For higher t, an anisotropic magnetoresistance typical for continuous ferromagnetic films was observed. [ABSTRACT FROM AUTHOR]

Co-W nanoparticles formed by sequential sputtering of Co on amorphous alumina substrate and subsequent W capping are studied by high resolution and by scanning transmission electron microscopies, and by superconducting quantum interference device magnetometry. The analysis is focused on W nominal thickness dependence. Results suggest the formation of amorphous Co-W alloy nanoparticles, whose magnetic moment per Co atom is systematically reduced as the nominal thickness of W capping layer increases. The Co-W nanoparticles show superparamagnetic behavior. The activation energy for moment reversal and the effective anisotropy are obtained. [ABSTRACT FROM AUTHOR]

Self-assembly has emerged as a suitable technique for tuning the properties of nanoparticles. In this work, we report the self-assembly of magnetosomes assisted by an external magnetic field. The magnetosomes are magnetite nanoparticles biomineralized by magnetotactic bacteria Magnetospirillum gryphiswaldense. These nanoparticles present truncated cubo-octahedral morphology with a mean diameter of ≈36nm and are surrounded by a lipid bilayer membrane with a thickness ≈2-4 nm. The use of the appropriate preparation conditions, such as initial colloidal concentration and magnetic fields applied during deposition allowed us to obtain very reproducible self-assembled 2D patterns. Homogeneous ensembles of magnetosomes onto silicon and carbon surfaces are composed of elongated structures in the form of wide chains that cover a large area of the substrates. Transmission electron microscopy image and off-axis electron holography showed the map of the stray magnetic fields produced by these assemblies. The induced magnetic anisotropy was analyzed by measuring the hysteresis loops of the assemblies at different angles in a magneto-optical Kerr effect magnetometer. The evolution of the coercive field and remanence verified the presence of well-defined patterns. The experimental results were analyzed on the based of a biaxial model. [ABSTRACT FROM AUTHOR]

W-capped Co nanoparticles dispersed in an alumina matrix are studied by means of high-resolution transmission electron microscopy, extended x-ray absorption fine structure, SQUID-based magnetic measurements, dc magnetization, ac magnetic susceptibility, and x-ray magnetic circular dichroism. Results show the formation of amorphous Co-W alloy nanoparticles, the magnetic properties of which are modified by the amount of W or Co present in the samples. The average Co magnetic moment depends on the number of W atoms surrounding it. Co-W particles show superparamagnetic behavior and are described as an array of noninteracting particles with random anisotropy axes and an average moment per particle proportional to the particle volume and to the average Co moment for each alloy composition. Values of the magnetic anisotropy constant of the particles are on the order of 106 erg/cm³, higher than that of bulk Co. Evidence of short-range ordering within each amorphous particle is found that provides insight of the origin of their magnetic anisotropy. [ABSTRACT FROM AUTHOR]